Intraoperative Doppler and real time sonography in neurosurgery

The Use of Intraoperative Microvascular Doppler in Vascular Neurosurgery: Rationale and Results-A Systematic Review

Surgical treatment of neurovascular lesions like intracranial aneurysms, arteriovenous malformations and arteriovenous dural fistulas is still associated with high morbidity. Several recent studies are providing increasing insights into reliable tools to improve surgery and reduce complications. Inadvertent vessel compromise and incomplete occlusion of the lesion represent the most possible complications in neurovascular surgery. It is clear that direct visual examination alone does not allow to identify all instances of vessel compromise. Various modalities, including angiography, microvascular Doppler and neurophysiological studies, have been utilized for hemodynamics of flow vessels in proper clipping of the aneurysm or complete obliteration of the lesion. We intended to review the current knowledge about the intraoperative microvascular Doppler (iMDS) employment in the most updated literature, and explore the most recent implications not only in intracranial aneurysms but also in neurovascular lesions like arteriovenous malformations (AVMs) and arteriovenous dural fistulas (AVDFs). According to the PRISMA guidelines, systematic research in the most updated platform was performed in order to provide a complete overview about iMDS employment in neurovascular surgery. Twelve articles were included in the present paper and analyzed according to specific research areas. iMDS employment could represent a crucial tool to improve surgery in neurovascular lesions. The safety and effectiveness of the surgical treatment of neurovascular lesions like intracranial aneurysm and other neurovascular lesions like AVMs and AVDFs requires careful and accurate consideration regarding the assessment of anatomy and blood flow. Prognosis may depend on suboptimal or incomplete exclusion of the lesion.

Decibel Decisions: The Concept of Intracranial Aneurysm Surgery With a Decibel Meter on Two Surgical Cases

The present cases were used to investigate the reliability of the intraoperative decibel meter as an objective method of clipping efficiency in cerebral aneurysm surgery and to assess the impact of this method on the surgical procedure itself. Different methodologies have been developed and applied to directly or indirectly evaluate the placement of a clip, for example, intraoperative digital subtraction angiography (DSA), intraoperative micro-Doppler ultrasonography, and, more recently, indocyanine green (ICG). We included two patients with a previously non-treated unruptured brain aneurysm. In both patients, intraoperative micro-Doppler was used in combination with a decibel meter app. Here, we present the cases of two patients. In patient one, the pre-clipping average sound level/equivalent continuous sound pressure level (Avg/Leq) was 96.7 dB, while the post-clipping Avg/Leq was 94.4 dB, indicating a reduction in sound level after clipping. Similarly, the pre-clipping time-weighted average noise level (TWA) was 1.2%, while the post-clipping TWA was 0.5%, indicating a decrease in exposure dose after clipping. In patient two, the average sound level for the post-clipping measurement (94.2 dB) was higher than the pre-clipping measurement (93.5 dB), but the difference was not statistically significant. These cases indicate the potential for using sound measurements as a reliable indicator of adequate aneurysm occlusion during clipping procedures. Further research is needed to confirm these findings.

Enhance Safety in Aneurysm Surgery: Strategies for Prevention of Intraoperative Vascular Complications

Complications during surgery for intracranial aneurysms can be devastating. Notorious pitfalls include premature rupture, parent vessel occlusion, local cerebral injury and brain contusion, and incomplete neck obliteration. These unfavorable intraoperative events can result in major neurological deficits with permanent morbidity and even mortality. Herein, the author highlights the relevant surgical strategies used in his daily practice of aneurysm surgery (e.g., aneurysm clipping with adenosine-induced temporary cardiac arrest), application of which may help prevent vascular complications and enhance surgical safety through reduction of the associated risks, thus allowing improvement of postoperative outcomes. Overall, all described methods and techniques should be considered as small pieces in the complex puzzle of prevention of vascular complications during aneurysm surgery.

Intraoperative utilization of Microvascular Doppler for the detection of intracranial venous structures during tumor resection - A technical note

BACKGROUND

Microvascular Doppler (MVD) has been widely used for the detection of arterial blood flow in the brain, especially during aneurysm clipping, vascular malformation resection, or bypass surgeries. However, the benefits obtained from early identification of intracranial sinuses and deep draining veins during tumor resection has not been reported.

METHODS

We reviewed the clinical data and imaging from our cases and conducted a systemic review of the medical literature using PubMed and keywords. Bibliographies of each result were evaluated to determine if additional reports describing the use of MVD during tumor resection could be found.

RESULTS

No reports were found in the literature where MVD was specifically used for venous identification during the resection of deep-seated brain tumors. In our patient cohort, MVD was used successfully to detect and ultimately allow immediate protection of large dural venous sinuses as well as smaller deep cerebral veins during tumor resection. Each patient developed no new venous infarcts and made a satisfactory recovery with no new postoperative neurological deficits.

CONCLUSION

MVD is a reliable tool for the intraoperative detection of intracranial venous blood flow to allow for quick identification and protection of venous structures. MVD is an additional safety measure for the patient as its accuracy in detecting venous structures is less susceptible to many of the inherent weaknesses of stereotactic neuro-navigation including the accompanying brain shift or anatomical distortion produced by long duration deep seated brain tumor resection.

Automatic intraoperative estimation of blood flow direction during neurosurgical interventions

PURPOSE

In neurosurgery, reliable information about blood vessel anatomy and flow direction is important to identify, characterize, and avoid damage to the vasculature. Due to ultrasound Doppler angle dependencies and the complexity of the vascular architecture, clinically valuable 3-D flow direction information is currently not available. In this paper, we aim to clinically validate and demonstrate the intraoperative use of a fully automatic method for estimation of 3-D blood flow direction from freehand 2-D Doppler ultrasound.

METHODS

A 3-D vessel model is reconstructed from 2-D Doppler ultrasound and used to determine the vessel architecture. The blood flow direction is then estimated automatically using the model in combination with Doppler velocity data. To enable testing and validation during surgery, the method was implemented as part of the open-source navigation system CustusX ( www.custusx.org ).

RESULTS

Ten patients were included prospectively. Data from four patients were processed postoperatively, and data from six patients were processed intraoperatively. In total, the blood flow direction was estimated for 48 different blood vessels with a success rate of 98%.

CONCLUSIONS

In this work, we have shown that the proposed method is suitable for fully automatic estimation of the blood flow direction in intracranial vessels during neurosurgical interventions. The method has the potential to make the understanding of the complex vascular anatomy and flow pattern more intuitive for the surgeon. The method is compatible with intraoperative use, and results can be presented within the limited time frame where they still are of clinical interest.

The Clinical Importance of Perforator Preservation in Intracranial Aneurysm Surgery: An Overview with a Review of the Literature

Clipping for intracranial aneurysms is done to achieve complete occlusion of the aneurysm without a remnant sac. Despite modern advancements of neurosurgical techniques, morbidity related to the clipping of intracranial aneurysms still exists. Clip occlusion of a parent artery or small hidden perforators commonly leads to permanent neurological deficits, and is a serious and unwanted complication. Thus, preserving blood flow in the branches and perforators of a parent artery is very important for successful surgery without postoperative morbidity and mortality. The aim of this review article is to discuss the consequences of perforator injury and how to avoid this phenomenon in aneurysm surgeries using intraoperative monitoring devices.

[Intraoperative indocyanine green fluorescence angiography in surgery of brain aneurysms. The first experience with using the technique and literature review]

Intraoperative blood flow assessment after aneurysm clipping has become a standard procedure in vascular neurosurgery worldwide. Intraoperative indacyanine green angiography (ICG) has recently been certified in Russia. Fifteen patients with aneurysms operated with ICG control in Burdenko NSI are described in present publication. ICG advantages and weaknesses are discussed along with alternative flow control techniques available now.

Model-based correction of velocity measurements in navigated 3-D ultrasound imaging during neurosurgical interventions

In neurosurgery, information of blood flow is important to identify and avoid damage to important vessels. Three-dimensional intraoperative ultrasound color-Doppler imaging has proven useful in this respect. However, due to Doppler angle-dependencies and the complexity of the vascular architecture, clinical valuable 3-D information of flow direction and velocity is currently not available. In this work, we aim to correct for angle-dependencies in 3-D flow images based on a geometric model of the neurovascular tree generated on-the-fly from free-hand 2-D imaging and an accurate position sensor system. The 3-D vessel model acts as a priori information of vessel orientation used to angle-correct the Doppler measurements, as well as provide an estimate of the average flow direction. Based on the flow direction we were also able to do aliasing correction to approximately double the measurable velocity range. In vitro experiments revealed a high accuracy and robustness for estimating the mean direction of flow. Accurate angle-correction of axial velocities were possible given a sufficient beam-to-flow angle for at least parts of a vessel segment . In vitro experiments showed an absolute relative bias of 9.5% for a challenging low-flow scenario. The method also showed promising results in vivo, improving the depiction of flow in the distal branches of intracranial aneurysms and the feeding arteries of an arteriovenous malformation. Careful inspection by an experienced surgeon confirmed the correct flow direction for all in vivo examples.

Intracranial pial arteriovenous fistula presenting with hemorrhage: a case report

Intracranial pial arteriovenous fistula (AVF) is a rare cerebrovascular malformation, which has a single or multiple arterial connections to a single venous channel without intervening nidus, and is different from arteriovenous malformation (AVM). We report on a case of a surgically treated pial AVF. A 15-year-old girl with an altered mental state was brought to our hospital. Computed tomography (CT) showed a subcortical hematoma of approximately 24 ml in her right temporal lobe. Cerebral angiography showed an AVF supplied by the right middle cerebral artery with early drainage into the Sylvian vein and the vein of Labbe. She underwent surgical treatment with feeding artery obliteration using a clip and hematoma removal. The patient was discharged without neurologic deficits. Despite the rarity of pial AVF, for correct diagnosis and treatment, neurosurgeons should recognize this condition. Pial AVF can be managed simply by disconnection of the shunt by surgery or endovascular treatment, and a good result can be achieved.

The role of intraoperative micro-Doppler ultrasound in verifying proper clip placement in intracranial aneurysm surgery

INTRODUCTION

Aneurysmal subarachnoid hemorrhage constitutes a clinical entity associated with high mortality and morbidity. It is widely accepted that improper clip placement may have as a result of incomplete aneurysm occlusion and/or partial or complete obstruction of an adjacent vessel. Various modalities, including intraoperative or postoperative digital subtracting angiography, near-infrared indocyanine green angiography, micro-Doppler ultrasonography (MDU), and neurophysiological studies, have been utilized for verifying proper clip placement. The aim of our study was to review the role of MDU during aneurysmal surgery.

METHODS

A literature search was performed using any possible combination of the following terms: "aneurysm," "brain," "cerebral," "clip," "clipping," "clip malpositioning," "clip repositioning," "clip suboptimal positioning," "Doppler," "intracranial," "microsurgery," "micro-Doppler," "residual neck," "ultrasonography," "ultrasound," and "vessel occlusion". Additionally, reference lists from the retrieved articles were reviewed for identifying any additional articles. Case reports and miniseries were excluded.

RESULTS

A total of 19 series employing intraoperative MDU during aneurysmal microsurgery were retrieved. All studies demonstrated that MDU accuracy is extremely high. The highest reported false-positive rate of MDU was 2 %, while the false-negative rate was reported as high as 1.6 %. It has been demonstrated that the presence of subarachnoid hemorrhage, specific anatomic locations, and large size may predispose to improper clip placement. Intraoperative MDU's technical limitations and weaknesses are adequately identified, in order to minimize the possibility of any misinterpretations.

CONCLUSION

Intraoperative MDU constitutes a safe, accurate, and low cost imaging modality for evaluating blood flow and for verifying proper clip placement during microsurgical clipping.

Monitoring techniques for prevention of procedure-related ischemic damage in aneurysm surgery

OBJECTIVE

To describe the application of intraoperative monitoring techniques during aneurysm surgery and to discuss the advantages and limitations of these techniques in prevention of postoperative neurologic deficits.

METHODS

Articles found in the literature through PubMed for the time frame 1980-2011 and the authors' personal files were reviewed.

RESULTS

Various techniques for detection of vascular insufficiency are available, including direct methods to measure cerebral blood flow and indirect methods to evaluate the integrity of neurologic pathways.

CONCLUSIONS

The choice of monitoring modality should be governed by the vessel and by the vascular territory most at risk during the planned procedure with proper awareness of the potential limits related to each technique. Aneurysm surgery monitoring should help to address issues of continuity and provide a morphologic and functional assessment. Although the use of monitoring devices is still not routine in aneurysm surgery and no standards have been established, combining different monitoring techniques is crucial to optimize aneurysm surgery and avoid or minimize complications.

Blood flow imaging: an angle-independent ultrasound modality for intraoperative assessment of flow dynamics in neurovascular surgery

OBJECTIVE

The objective of this study was to investigate the clinical applicability of navigated blood flow imaging (BFI) in neurovascular applications. BFI is a new 2-dimensional ultrasound modality that offers angle-independent visualization of flow. When integrated with 3-dimensional (3D) navigation technology, BFI can be considered as a first step toward the ideal tool for surgical needs: a real-time, high-resolution, 3D visualization that properly portrays both vessel geometry and flow direction.

METHODS

A 3D model of the vascular tree was extracted from preoperative magnetic resonance angiographic data and used as a reference for intraoperative any-plane guided ultrasound acquisitions. A high-end ultrasound scanner was interconnected, and synchronized recordings of BFI and 3D navigation scenes were acquired. The potential of BFI as an intraoperative tool for flow visualization was evaluated in 3 cerebral aneurysms and 3 arteriovenous malformations.

RESULTS

The neurovascular flow direction was properly visualized in all cases using BFI. Navigation technology allowed for identification of the vessels of interest, despite the presence of brain shift. The surgeon found BFI to be very intuitive compared with conventional color Doppler methods. BFI allowed for quality control of sufficient flow in all distal arteries during aneurysm surgery and made it easier to discern between feeding arteries and draining veins during surgery for arteriovenous malformations.

CONCLUSION

BFI seems to be a promising modality for neurovascular flow visualization that may provide the neurosurgeon with a valuable tool for safer surgical interventions. However, further work is needed to establish the clinical usefulness of the proposed imaging setup.

Spontaneous pial single-channel arteriovenous fistulae with angiographically occult small feeding arteries: case report

BACKGROUND

Pial single-channel arteriovenous (AV) fistulae are usually cured by interrupting only the feeding arteries identified in cerebral angiography.

CASE DESCRIPTION

A 27-year-old woman presented after 3 complex partial seizures due to a pial single-channel AV fistula with the varix located in the right temporal lobe. When all feeding arteries identified by preoperative cerebral angiography were temporarily occluded, varix blood flow was confirmed with Doppler ultrasonography. Many small feeding arteries were identified, and the varix was dissected and removed. The postoperative course was uneventful and postoperative cerebral angiography revealed no abnormal vascular lesions.

CONCLUSION

Pial single-channel AV fistulae are not always cured by interrupting only the feeding arteries identified in cerebral angiography and might require varix removal.

Intraoperative ultrasound using phase inversion harmonic imaging: first experiences

OBJECTIVE

To study the feasibility of intraoperative ultrasound using the phase inversion harmonic imaging (PIHI) technique.

METHODS

Eight patients with intracranial middle cerebral artery aneurysms and five patients with arteriovenous malformations were studied after written informed consent. A first ultrasound study was performed through the intact dura mater after cranial trepanation to assess the pathology, its feeding artery, and downstream segments. A second ultrasound study was performed immediately after intervention to monitor the success of the procedure. All patients were studied using a Siemens Sonoline Antares ultrasound machine (Siemens Medical Solutions USA, Inc., Malvern, PA) before and after intravenous administration of an ultrasound contrast agent (Optison; GE Healthcare, Milwaukee, WI). Other than conventional brightness mode, PIHI is sensitive to the nonlinear acoustic response of tissue, and especially to ultrasound contrast agent microbubbles. The latter enables contrast-specific vascular imaging.

RESULTS

PIHI provided anatomically detailed information. In combination with an ultrasound contrast agent, angiography-like views of the vascular pathologies, including their surrounding vessels, could be obtained. Flow velocities in afferent and downstream vascular segments, as well as inside the pathology, could be assessed. Flow dynamics inside the aneurysm sac or the arteriovenous malformation could be studied in real-time. Postintervention, contrast-enhanced PIHI could be used to immediately monitor the success of the surgical procedure.

CONCLUSION

PIHI enables intraoperative visualization and morphological assessment of neurovascular pathologies, such as middle cerebral artery aneurysms or arteriovenous malformations. In combination with an ultrasound contrast agent, the flow dynamics of these lesions can be displayed in real-time.

Intraoperative microvascular Doppler in intracranial aneurysm surgery

OBJECTIVE

The usefulness of intraoperative microvascular Doppler (IMD) in preventing an incorrect placement of the clip during intracranial aneurysm surgery is described. Such incorrect placement of the clip may cause new bleeding or ischemic accident as a consequence of incomplete exclusion of the aneurysm or stenosis/occlusion of the parent and/or adjacent arteries.

METHODS

One hundred thirty patients, harboring 136 aneurysms, were operated on using IMD. IMD study was performed on the aneurysm and adjacent arterial vessels before and after the clip placement. Mechanical arterial spasm was treated by topical sodium nitroprusside (SNP) and its efficacy verified by IMD.

RESULTS

In 55 aneurysms (42.3%), IMD was helpful in understanding the microvascular anatomy before clip placement. Complete exclusion resulted in 129 aneurysms (94.9%). In 5 cases (3.7%) in which IMD revealed a persistent blood flow in the aneurysm, the clip was repositioned. In 2 cases (1.4%), we obtained false-negative results. In 25 cases (18.3%) in which IMD data documented a severe flow reduction in the vessel harboring the aneurysm or in the vessel originating very close to the aneurysm neck, the clip was repositioned. There were no complications due to the use of IMD. In 20 patients (15%) in which IMD revealed arterial spasm by surgical manipulation, topical SNP was followed by resolution of the spasm.

CONCLUSION

IMD is a feasible, safe, and very reliable technique in aneurysm surgery. Compared to other procedures such as intraoperative angiography, the cost efficiency of IMD is favorable.

Intraoperative Doppler to Measure Cerebrovascular Resistance as a Guide to Complete Resection of Arteriovenous Malformations

OBJECTIVE:

Intraoperative color Doppler ultrasound has been used to locate arteriovenous malformations (AVMs). We describe the use of spectral Doppler to measure flow resistance and resistive index (RI) of vessels around the nidus to distinguish feeding arteries from en passant and normal vessels. This is particularly helpful in small AVMs and aids in the identification of normal vessels and completeness of resection by ruling out persistent low RI flow.

METHODS:

Seven patients with AVMs underwent resection. Spectral Doppler applied to the vessels in proximity to the AVM, along with calculated RI, was used to identify feeding arteries and draining veins. After presumed surgical resection of the AVM, pre-resection and postresection RIs were compared to identify residual AVM. Postoperative angiography was performed in all seven patients to confirm complete resection of the AVM.

RESULTS:

The mean pre-resection RI of vessels feeding the AVM was 0.34 (±0.01). In five patients without residual nidus on the basis of postresection color Doppler and postoperative angiogram, the postresection RI was 0.62 (±0.04). In two patients, the postresection scan identified a nidus with persistent low RI flow. Once residual AVM was resected, the RI became significantly higher. A postoperative angiogram confirmed complete resection of the AVM in all patients.

CONCLUSION:

Intraoperative duplex Doppler allowed more accurate localization of the AVM nidus. RI of the vessels around the AVM helped to distinguish vessels feeding the AVM from en passant vessels. Furthermore, comparison of pre-resection and postresection RI accurately indicated the completeness of resection.

Monitoring of motor evoked potentials compared with somatosensory evoked potentials and microvascular Doppler ultrasonography in cerebral aneurysm surgery

OBJECT

The aims of this study were to compare the efficiency of motor evoked potentials (MEPs), somatosensory evoked potentials (SSEPs), and microvascular Doppler ultrasonography (MDU) in the detection of impending motor impairment from subcortical ischemia in aneurysm surgery; to determine their sensitivity for specific intraoperative events; and to compare their impact on the surgical strategy used.

METHODS

Motor evoked potentials, SSEPs, and MDU were monitored during 100 operations for 129 aneurysms in 95 patients. Intraoperative events, monitoring results, and clinical outcome were correlated in a prospective observational design. Motor evoked potentials indicated inadequate temporary clipping, inadvertent occlusion, inadequate retraction, vasospasm, or compromise to perforating vessels in 21 of 33 instances and deteriorated despite stable SSEPs in 18 cases. Microvascular Doppler ultrasonography revealed inadvertent vessel occlusion in eight of 10 cases and insufficient clipping in four of four cases. Stable evoked potentials (EPs) allowed safe, permanent vessel occlusion or narrowing despite reduced flow on MDU in five cases. Two patients sustained permanent and 10 showed transient new weakness, which had been detected by SSEPs in two of 12 patients and MEPs in 10 of 11 monitored cases. The surgical strategy was directly altered in 33 instances: by MEPs in 16, SSEPs in four, and MDU in 13.

CONCLUSIONS

Monitoring of MEPs is superior to SSEP monitoring and MDU in detecting motor impairment, particularly that from subcortical ischemia. Microvascular Doppler ultrasonography is superior to EP monitoring in detecting inadvertent vessel occlusion, but cannot assess remote collateral flow. Motor evoked potentials are most sensitive to all other intraoperative conditions and have a direct influence on the course of surgery in the majority of events. A controlled study design is required to confirm the positive effect of monitoring on clinical outcome in aneurysm surgery.

Intraoperative microvascular Doppler ultrasonography in cerebral aneurysm surgery

OBJECTIVES

Outcome of surgical treatment of cerebral aneurysms may be severely compromised by local cerebral ischaemia or infarction resulting from the inadvertent occlusion of an adjacent vessel by the aneurysm clip, or by incomplete aneurysm closure. It is therefore mandatory to optimise clip placement in situ to reduce the complication rate. The present study was performed to investigate the reliability of intraoperative microvascular Doppler ultrasonography (MDU) in cerebral aneurysm surgery, and to assess the impact of this method on the surgical procedure itself.

METHODS

Seventy five patients (19 men, 56 women, mean age 54.8 years, range 22-84 years) with 90 saccular cerebral aneurysms were evaluated. Blood flow velocities in the aneurysmal sac and in the adjacent vessels were determined by MDU before and after aneurysm clipping. The findings of MDU were analysed and compared with those of visual inspection of the surgical site and of postoperative angiography. Analysis was also made of the cases in which the clip was repositioned due to MDU findings.

RESULTS

A relevant stenosis of an adjacent vessel induced by clip positioning that had escaped detection by visual inspection was identified by Doppler ultrasonography in 17 out of 90 (18.9%) aneurysms. In addition, Doppler ultrasound demonstrated a primarily unoccluded aneurysm in 11 out of 90 (12.2%) patients. The aneurysm clip was repositioned on the basis of the MDU findings in 26 out of 90 (28.8%) cases. In middle cerebral artery (MCA) aneurysms, the MDU results were relevant to the surgical procedure in 17 out of 44 (38.6%) cases. Whereas with aneurysms of the anterior cerebral artery significant findings occurred in only five of 32 cases (15.6%; p<0.05). The clip was repositioned on the basis of the MDU results in 18 out of 50 (36%) aneurysms in patients with subarachnoid haemorrhage (SAH) grade I-V compared with only eight out of 40 (20%) aneurysms in patients without SAH (p<0.05).

CONCLUSIONS

MDU should be used routinely in cerebral aneurysm surgery, especially in cases of MCA aneurysms and after SAH. Present data show that a postoperative angiography becomes superfluous whenever there is good visualisation of the "working site" and MDU findings are clear.

History of intraoperative ultrasound

Intraoperative ultrasound (IOUS) using A-mode or non-real-time B-mode imaging started in the 1960s; however, it was not widely accepted mainly because of difficulty in image interpretation. In the late 1970s, IOUS became one of the topics in the surgical communities upon the introduction of high-frequency real-time B-mode ultrasound. Special probes for operative use were developed. In the 1980s, all over the world the use of IOUS spread to a variety of surgical fields, such as hepatobiliary pancreatic surgery, neurosurgery, and cardiovascular surgery. IOUS changed hepatic surgery dramatically because IOUS was the only modality that was capable of delineating and examining the interior of the liver during surgery. After 1990, color Doppler imaging and laparoscopic ultrasound were incorporated into IOUS. Currently, IOUS is considered an indispensable operative procedure for intraoperative decision-making and guidance of surgical procedures. For better surgical practice, education of surgeons in the use of ultrasound is the most important issue.

Intraoperative monitoring with pulse Doppler ultrasonography in transsphenoidal surgery: technique application

We describe an intraoperative use of pulse Doppler ultrasonography in transsphenoidal surgery to prevent mechanical vascular injury, particularly to the intracavernous portion of the internal carotid artery. This system is integrated by connection to a video processor. The use of Doppler sonography provided real-time measurement of arterial or venous flow velocity and source of flow by both real-time sonograms and sound frequencies. With the use of a microprobe, 1 mm in diameter, vessels located within 7 mm from the tip of the probe could be easily, rapidly, and noninvasively detected, without disturbing operative field. Furthermore, both the size and the distance of a vessel could be measured by turning the dial of Doppler signal gain from initially waxing to waning Doppler sounds, because the acoustic sounds were adjusted to the axial flow of each vessel in 0.1-mm increments. Our intraoperative monitoring enhanced operative safety with technical simplicity and reliability.

Pre- and intraoperative methods of controlling cerebral circulation in giant aneurysm surgery

The surgical treatment of giant aneurysms usually requires temporary clipping of the aneurysmatic vessel. In planning the surgical approach and in applying temporary clips, the surgeon must consider collateral circulations. The functional integrity of the collateral vessels frequently decides the patient's outcome. In 8 patients with internal carotid artery giant aneurysm, measurements of blood flow velocities in the ipsilateral middle cerebral artery were performed preoperatively with transcranial Doppler ultrasound (TCD) during manual occlusion of the carotid artery at the neck. Three different perfusion patterns were established, and each collateral capacity was rated as insufficient, temporarily sufficient, or long-term unproblematic. Surgical strategies were conceived. In one patient with giant aneurysm of the middle cerebral artery the temporary occlusion test was not carried out preoperatively. Intraoperatively, collateral circulation was controlled using microvascular Doppler sonography (MVD). In 8 cases cortical blood flow (CoBF) was monitored by thermal diffusion flow probe and/or laser Doppler. In some cases, the complex pathological anatomy required a change in surgical strategy and a new MVD determination of collateral capacity. Despite these precautions 2 patients suffered ischemia of the basal ganglia and the white matter.

Intraoperative use of Doppler ultrasound and endoscopic monitoring in the stereotactic biopsy of malignant brain tumors. Technical note

An intraoperative monitoring tool is described that prevents mechanical injury to intracerebral vessels during stereotactic surgery. The method, which combines pulse Doppler ultrasonography and fiberendoscopy, allowed stereotactic biopsy to be performed without serious intracerebral bleeding in 25 patients with hypervascular malignant brain tumors, 13 with glioblastoma multiforme, five with anaplastic astrocytoma, five with metastatic tumor, and two with malignant lymphoma. The ultrasound apparatus has a built-in fast-Fourier transformation system analyzer and an improved filtering system that provide real-time measurement of blood flow velocity. The source of flow (arterial or venous) could be identified by both real-time sonography and acoustic signal frequencies. It was possible to measure the size and distance of a vessel by adjusting the Doppler signal gain dial from initially waxing to waning sounds, because the acoustic signal was adjusted to the axial flow of each vessel in 0.1-mm steps. Each of three Doppler probes (1 mm, 2 mm, and 3 mm in diameter) fit through the outer cannula of the biopsy needle. Vessels located within 7 mm from the tip of these probes could be detected easily and rapidly, so the biopsy needle could be advanced safely to the desired target in 7-mm steps. If sonograms revealed blood flow, indicating the presence of larger vessels in the intended stereotactic trajectory, the angle of the needle was changed slightly to avoid vascular injury. Because the fiberendoscope was connected to a video processor, the vessel could be visualized at a higher magnification on the video display, unless there was active bleeding. This technically simple and reliable system enhances operative safety while maintaining accuracy.

Practical application of intraoperative ultrasound imaging

Intraoperative real-time ultrasound imaging (US) was used in over 500 patients to investigate which of the previously considered applications are of practical use in everyday neurosurgery. During all intraoperative applications for a wide variety of pathological conditions, small deep-seated as well as subcortically located lesions were detected with accuracy; in many instances they could be approached through smaller surgical exposures. US guidance was accurate in 209 cases for the stereotactic introduction of needles or endoscopes into various lesions: thus burrhole evacuation was performed on 148 intracerebral haematomas; in 16 patients endoscopic biopsy and resection of ventricular tumours was performed as well as biopsies of 39 hemispheric brain tumours and aspiration of a brain abscess in 6 instances. Seventy six gliomas were investigated by US imaging; the frequently unclear boundary between tumour and surrounding oedema was not better visualized than with CT or MRI. Moreover, US imaging for the detection of residual tumour towards the end of operation was unreliable. Postoperative imaging through burrholes or other cranial defects was mostly of unacceptably low quality for therapeutic decision making.

Intraoperative measurement of cortical blood flow adjacent to cerebral AVM using laser Doppler velocimetry

Standard methods for measurement of cerebral blood flow (CBF) are not optimal for continuous intraoperative recording. Laser Doppler velocimetry has been used for evaluation of microcirculatory flow in a variety of human tissues, including skin, muscle, and retina. The authors report the use of this technique for measuring flow in human cerebral cortex. The physiological changes associated with excision of a cerebral arteriovenous malformation are interpreted using CBF recorded intraoperatively with the laser Doppler probe.